This invention relates to a novel apparatus and process for treating sewage and, in particular, sewage sludge.
Traditionally, sewage and specifically sewage sludge has been difficult to treat because it is, almost by definition, extremely variable in composition. In addition to human liquid and solid organic waste, the sludge to be treated in accordance with the present invention may include industrial and commercial sludge which is susceptible to aerobic treatment. In general, the present invention provides a means and process for highly efficient interaction of sludge particles with oxygen, in the form of O.sub.2 gas and/or O.sub.3 gas.
The present invention preferably employs the use of hyperbaric vessels containing pressurized oxygen and the sludge, and provides means for increasing the surface area of sludge to be treated and the interaction time in which sludge is oxygenated compared to prior art apparatus and processes.
A further feature of the present invention resides in the substantially infinite adjustability of the various components of the apparatus and process so that they can be finely tuned at any time and adjusted automatically, semi-automatically and/or manually to treat different types, compositions and thicknesses of various sludges without requiring the use of alternate equipment.
The present invention is an important advancement in the treatment of sewage sludge, generally consisting of four basic steps. Preferably, the first step is to adjust the pH of the sludge to an appropriate acidic level, so that it is more susceptible to aerobic treatment. Second, the sludge is dispersed in an oxygen-rich and, preferably, a pressurized atmosphere. Third, the oxygen reacts directly or indirectly with contaminants in the sludge to convert them into stable materials. Fourth, bacteria contained in the sludge are rendered harmless so that the treated sludge may be disposed of in landfill or other areas without significant adverse environmental consequences.
The present invention is intended primarily for treatment of activated sludge, namely, waste from domestic, commercial and industrial sources which create a biologically degradable material. A batch of the pH adjusted waste to be treated is divided into small droplets and the droplets are dispersed within a pressure vessel where they are oxygenated by being exposed to oxygen (O.sub.2) and ozone (O.sub.3) for a substantial period of time. The Biological Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD) of the waste are substantially saturated and satisfied. The addition of ozone produces an almost complete destruction and elimination of coliform, fecal coliform, salmonella and other harmful bacteria from the batch of sludge being treated. Although the coliform and fecal coliform bacteria are not in themselves particularly harmful, when they are present, it is recognized that other harmful bacteria are present. Thus, when the coliform and fecal coliform bacteria are destroyed, it is an indication that the other harmful bacteria, which are more difficult to detect, are also destroyed.
Further background concerning the treatment of activated sludge is set forth, for example, in U.S. Pat. No. 3,724,667, issued Apr. 3, 1973 to McKinney. The present invention is an improvement over the McKinney activated sludge treatment apparatus and process. The heart of McKinney's system is the spraying of sludge into a pressurized atmosphere rich in oxygen. As explained in the patent, McKinney's system is based upon the belief that the combination of an oxygen-rich gas and the increased pressure increases the efficiency of the oxygen transfer to the droplets of sludge within the enclosed treatment vessel.
Another prior art technique for treating sewage in a pressurized oxygen-rich atmosphere is set forth in U.S. Pat. No. 3,772,188, issued Nov. 13, 1973 to Edwards. In the Edwards system, sewage is transported into a vessel and impacted against a rotating comminutor which breaks the sewage into small particles for interaction with the pressurized oxygen atmosphere.
Another pertinent prior art patent is U.S. Pat. No. 1,790,975, issued Feb. 3, 1931 to Dallas, et al. This patent treats sewage by causing it to be aerated after it has been distributed through distributor heads to the atmosphere above the level of the sewage. After it is sufficiently aerated, it is discharged. Two different embodiments of distributor heads are illustrated and described in this patent.
By the present invention, small sludge particles are created efficiently and means are provided for greatly enhancing the surface area of the sludge to be treated and the time of interaction of finely divided sludge particles with oxygen-rich atmosphere, preferably in a pressurized environment. The present invention is believed to be extremely well suited to large scale treatment systems and very large interaction vessels. By means of the substantially infinite adjustability of its various components, the present invention is also very effective in treating sludge which can and does vary in composition almost continuously.